In bipolar devices containing a wide bandgap semiconductor material such as SiC or unipolar devices containing a wide bandgap semiconductor material such as SiC and caused to perform bipolar operation such as that occurring with movement of minority carriers, high energy is generated at the time of hole-electron recombination due to the wide bandgap. Such recombination occurs near basal plane dislocations (BPDs) and thus, a phenomenon is observed in which the high energy causes defects and translocations to become stacking faults and expand, whereby degradation phenomena such as increases in ON resistance are observed.
Conventionally, degradation is prevented by a conversion layer structure that at a very high ratio (e.g., 99%, etc.), converts basal plane dislocations (BPDs) present at an interface of a substrate and an epitaxial layer, into threading edge dislocations (TEDs), etc., which have a low impact on electrical characteristics (for example, refer to Patent Document 1).
Further, a scheme has been proposed in which Z1/2 centers (carbon vacancy defect energy-level) at a density lower than the dopant concentration is introduced in a drift layer that is a low-dopant region constituting a breakdown voltage maintaining layer, whereby without significantly affecting unipolar operation, killing of minority carriers at the time of bipolar operation decreases the minority carriers that reach the substrate decrease and no high energy due to recombination to BPDs in the substrate is generated (for example, refer to Patent Document 2).